Control circuit for gas triodes



Feb. 24, 1942. MO-NTGOMERY $273,978

common CIRCUIT FOR GAS TRIODES Filed March 31, 1939 Patented Feb. 24, 1942 CONTROL CIRCUIT FOR GAS TRIODES Andrew P. Montgomery, Narberth, Pa., assignor, by mesne assignments, to Philco Radio and Television Corporation, Philadelphia, Pa., a

corporation of Delaware Application March 31, 1939, Serial No. 265,328 In Great Britain August'26, 1938 13 can... (Cl.250-27) This invention relates to controllcircuits for grid-controlled gas triodes or thyratrons. .The

invention is particularly directed to those cir-, cuits wherein the gas triode is employed in the.

control of electromechanical relays and the like and wherein alternating current power is supplied to the plate circuit of the gas triode.

One object of the invention is to provide circuits for such a triode which result in a more reliable and positive control than has heretofore been possible.

' 'Another object of the invention is to providea means for maintaining a continuous current in the load circuits of gas triodes supplied only with alternating current plate power. I

A further object of the invention is to provide a reliable control circuit for gas triodes wherein suitablealternating current voltages are applied to both grid and plate in such' phase and mag nitude that the gas triode is maintained in a non-ionized condition, but wherein thel'triode may be fired by the application to the input circuit of a relatively feeble radio frequency signal.

Still another object of the invention isto'provide a gas triode control circuit wherein the signal applied to the input circuit of the triode comprises a low frequency alternating current voltage as well as a direct current component on which may be superimposed ahigh or radiofrequency control-signal, said direct current .component being a function of the state of conductivity of the gas triode, as wellas of the presence or absence of the radio frequency control signal.

Accordingly, the invention provides in a control circuit for gas triodes and the like, a gas triode having an input electrode and an output electrode, means for applying alternating current voltages of predetermined phases and magnitudes to said electrodes, a load device connected to said output electrode, means for applying a bias voltage to said input electrode, means for applying a radio frequency sig'nal'to saidinput electrode, the space path of said triode being rendered conducting in the presence of said signal for positive alternations only of the output electrode supply voltage, and means associated with said load device for maintaining a fiow of current, therein during the negativev alternations of said output electrode supply voltage.

In the accompanying drawing:

Fig. 1 illustrates a specific embodiment of the invention;

,Fig. 2 is an illustrative diagram of several voltages present in the circuit; and

Fig. 3' is adiagram representing the voltages corresponding to those of Fig. 2 under different conditions.

In Fig. 1, a transformer 2whose right-hand fterminals may be connected to any suitable alternating current power source, is employed to supply plate voltage to the plate of the gas triode l by way of the load 3, and grid voltage to grid of the triode by way of the resistors 6 and 9 and the secondary of the transformer 8. The cathode is shown. connected to a tapped point on the transformer. Separate transformers may, of course, be employed to supply the grid and plate voltages if desired. The relative phase of the two voltages may be fixed by means of a suitable phase shifting network which may comprise resistor 6 and acondenser 1. The grid electrode is supplied with a self-bias voltage by means of a resistance-capacity network 9-H), the specific operation of which will be described hereinafter.

Associated with the load impedance 3 is an energy storing element such as the condenser 5 and, if desired, a resistor 4. The time constant of this circuit will preferably be greater than the period of the plate voltage so as to insure a more or less "continuous flow of current through the. load 3, as will be explained hereinafter. The resister 4, in addition to having an effect on the time constant of the circuit 3+-45, may further be employed to limit the peak current through the triode, since in some instances the condenser 5 may have a comparatively high capacity.

A suitable signal may be applied to the input circuit of the gas triode by way of the transformer 8 Which may be tuned if desired. The input terminals of the transformer 8 may be supplied with such a signal from any suitable source such as a signal receiving system.

.Thus, it is seen that the grid-cathode circuit of the gas triode may be supplied simultaneously with three separate voltages,namely, an alternating current component'from the transformer 2, a direct current component due to rectified grid current, and a signal component-from the I which the triode will not fire, the alternating current grid voltage which is applied to the grid by way of the phase shifting network 6-1, the direct current grid voltage, and the composite gridvoltage which is the sum of the grid voltages here mentioned and the radio frequency signal voltage supplied by the transformer 8. Since the characteristics of gas triodes or thyratrons are well known to those skilled in the art, it is believed to be unnecessary to review their theory.

Referring first to Fig. 2, it may be seen that when no radio frequency signal is present, the grid voltage will be more negative than the critical voltage necessary to prevent ionization of the gas in the triode I. Consequently, there will be no current flow in the plate circuit of the triode. However, when a radio frequency signal is present, as shown, the grid will become momentarily less negative than this critical voltage, so that the gas in the tube may ionize and a current flow through the load 3 for the duration of the positive alternation of the plate voltage wave. This current will also charge the condenser 5. Hence, during the negative alternation of the plate voltage wave when no space current flows through the triode, the charge on the condenser Will leak off through the load impedance 3 so as to maintain a continuous current therein. It is, of course, understood that upon the. cessation of the radio frequency signal, the gas triode Will cease to conduct, and will remain in. this state until the radio frequency signal again appears as hereinbefore described.

The phase-shifting network 6-! is preferably adjusted to provide a phase difference between the alternating current grid and plate voltages of such an order that firing of the gas triode in the presence of a radio frequency signal will occur at the beginning of the alternating current plate cycle rather than at a later time. This preferred condition is shown both in Figs. 2 and 3. If firing occurs too late in the cycle, the available load current may be seriously limited.

Assuming now that the cycle of operation shown in Fig. 2 has just been completed, and that the radio frequency signal persists, it will be seen that, owing to the aforementioned time constant of the circuit 345, the charge on the condenser will not have been fully reduced to zero when the plate voltage again swings positive. Consequently, the plate-cathode voltage will be less than it was in the corresponding stage of the foregoing cycle. Hence, the critical voltage will be less negative than in the foregoing cycle (see Fig. 3), and hence the grid signal shown in Fig. 2 will no longer be able to control the firing of the tube, the grid being too negative to allow ionization. The result of this wouldbe that the triode might fire only on every second or third positive plate voltage alternation and thus the average current through the load impedance would be materially reduced.

The superposition of the grid Voltages of Fig. 2 on the plate and critical voltages of Fig, 3 will disclose that this efiect may be compensated for by decreasing the negative grid bias. This has been accomplished, according to the present invention, by making the time constant of the resistance-capacity combination 9l0 of the order of, or preferably greater than the period of the alternating voltage supply. Then when the tube ionizes under conditions represented in Fig. 2, the negative grid will attract positive ions, thereby effectively reducing the direct current grid bias. In Fig. 3 this decreased grid bias is indicated, and it is clearly seen that ionization is again possible in spite of the decreased criticalgrid voltage also shown in Fig. 3.

Thus, the invention provides a means for supplying continuous direct current to a load in the plate circuit of a gas triode, and further provides a means to insure the reliable control of the triode by means of a radio frequency input signal.

A further aspect of the control circuit contributes to its reliability. Thus, assume that the high frequency signal impressed on the triode grid by way of the transformer 8 consists of a group of discrete high frequency wave trains, each having a duration, say, of one tenth second, and separated from the following wave train by a comparable length of time. Assume that the load 3 is a suitable relay designed to be energized by the gas triode, the energization to last for the duration of each discrete wave train. Assume further, by way of example, that five such wave trains are transmitted and that it is desired that the relay record each of the five wave trains Without error. Conceivably these trains might arrive in such a weakened condition that the gas triode would fire only three times, the relay, therefore, being able to count only three units. However, the present invention tends to prevent such an occurrence, the relay either counting all or none of the received trains. This highly favorable situation is brought about as follows: Suppose that the first of a series of five wave trains arrives but is of such low signal strength as to fail to produce ionization. In this event, the effect of the signal upon the input circuit of the gas triode is to increase the electron current flowing through the circuit 9-"), and thus to increase the negative grid bias. The result is that the following wave trains in the series have even less chance of firing the triode than did the first, and hence while the relay 3 is not actuated at all, it also fails to give an inaccurate indication. On the other hand, as indicated hereinbefore, if the first wave train fires the triode, the grid bias is decreased, and hence possibility of following trains failing to fire the triode is very remote. Thus, a relay or other suitable utilization means energized by the circuit of the present invention tends to give either a correct indication of the received signals, or no indication at all.

An application of the present invention similar to that described is disclosed in the copending application of E. 0. Thompson and D. Grimes, Serial No. 220,366, filed July 20, 1938, wherein the gas triode is employed to energize a step-bystep switch in a remote control circuit.

In a specific embodiment of the invention, which is not to be taken as limiting the invention, the following values were employed:

Resistor 9=50,000 ohms Resistor 6: 4,000 ohms Condenser 10:0.5 Mfd. Condenser 7:0.1 Mfd. Condenser 5:16 Mfd. Resistor 4:150 ohms Obviously, the invention is capable of various other modifications and embodiments without departing from its scope as defined in the appended claims.

I claim:

- 1. In a control circuit for gas triodes and the like, a gas triode having an input electrode and an output electrode, means for applying low frequency alternating current voltages of predetermined different phases and substantially fixed magnitudes to said electrodes, a load device connected to said output electrode, means for applying a bias voltage to said input electrode, means for applying a higher frequency signal to said input electrode, the space path of said triode being renderedconducting in the presence of said signal for positive alterations only of the output electrode supply voltage, and means associated with said'load device for maintaining a. flow of current therein during the negative alterations of said output electrode supply voltage.

2. In a control circuit for gas triodes and the voltage, a'sourceof alternating current voltage like, a gas triode having a grid, a cathode, and

a plate, a source of low frequency alternating current voltage, means for applying a part ofsaid voltage to said plate, phase shifting means forapplying another part of saidflvoltageto said grid, said phase shifting means including a resistor and a condenser, a load device connected to said plate, means for developing a self-bias voltage, means for applying said bias voltage I tosaid gridgmeane for applying a radio frequen cy signal to said grid; the space path of said triode being rendered conducting in the presence of said signal for positive alternations only of the plate voltage, and means associated with nection to said platev a relatively large condenser in shunt with said'load circuit, means including a resistor and condenser included in the voltage supply connection to said grid for developing a self-bias between said grid and cathode, and means for applying a radio frequency signal to said grid, the space path of said triode being rendered conducting in the presence of said signal for positive alternations only of the output electrode supply voltage.

4. In a control circuit as claimed in claim 3, the provision of a plate current limiting resistor in series with the relatively large shunt condenser.

.5. In a control circuit for gas triodes and the like, a gas triode having a cathode, an input electrode, and an output electrode, an output circuit and output load connected to said output electrode, means for supplying a low frequency alternating current voltage to said output electrode,

a source of bias voltage, a source of high frequency signal voltage, a source of alternating current voltage of said first-mentioned frequency and having a fixed phase and magnitude relationship with said first named alternating current voltage, and means for serially connecting said three voltage sources between said input electrode and said cathode, the space path of said triode being rendered conducting for positive alternations of said output electrode supply voltage but only in the combined presence of voltages from said three voltage sources.

6. In a control circuit for gas triodes and the like, a gas triode having a cathode, an input electrode, and an output electrode, an output circuit and an output load connected to said output electrode, means for supplying a low frequency alternating current voltage in series with said cathode, output electrode, output circuit and load, a source of bias voltage, a source ofsignal voltage, said signal voltage having a high frequency connected between said cathode and the other terminal of said phase-shifting network, a

havinga fixed predeterminedphase and magni-. tuderelationship with said first'named alternate 1 ing current voltage. means for serially'connecting said three voltage sources between said inputelectrode' and said cathode, the space path of said triode being -rendered conducting for positive alternations of said output electrode supply voltage but only in the combined presence of voltages from said three voltage sources, and capacitive means associated with said output load for maintaining a flow of current therein during the negative alternations of said output electrode supply voltage.

7. In a control'circuit for gas triodes and the like, a gas triode having a grid, a'cathode, and

a plate, a load impedance having one end connected to said plate, a capacitive reactance shunted across said impedance, a source of low fre-' quency alternating current of fixed amplitude connected between the other end of said load im-- pedance and said cathode, a phaseeshifting network having one terminal connected to said cathode, a second source of alternating current of said low frequency connected between said cathode and the other terminal of said phaseshifting network, aisour'ce of intermittent high frequency signals, said last-named source being connected'between said grid and a point on said phase-shifting network; and a resistance-capacitanc'e'self-biasing means included in said lastnamed connection, said last-named means having a'time constant of the order of the period of said low frequency alternating current. v

8. In a control circuit for gas triodes and the like, a gas triode having a grid, acathode, and a plate, a load impedance having one end connected to said plate, a capacitive reactance shunted across said impedance, a source of low frequency alternatingcurrent of fixed'amplitude connected betweenthe other end of said load impedanceand' said cathode, a phase-shifting network having one terminal connected to said cathode, a second source of alternating current of said low fresource of intermittent high frequency signals, said last-named source being connected between said grid and a point on said phase-shifting network, and a resistance-capacitance self-biasing means included in said last-named connection, said last-named means having a time constant greater than the period of said low frequency alternating current.

9. In a control circuit for gas triodes and the like, a gas triode having a grid, a cathode, and a plate, a load impedance having one end connected to said plate, a capacitive reactance shunted across said impedance, a source of low frequency alternating current of fixed amplitude connected between the other end of said load impedance and said cathode, a phase-shifting network comprising fixed impedances and having one terminal connected to said cathode, a

quency with respect to said first mentioned shunted by acondenser serially included in said last-named connection, said last-named means having a time constant whose magnitude is at least of the'orderfof the period of said low frequency alternating current.

10. In a control circuit for gas-triodes and the like, a gas triode having ,a grid, a cathode, and a plate, a load impedance having one end connected to said plate, a source oflow frequency alternating current of fixed amplitude connected between the other end of said load impedance and said cathode, a phase-shifting network having, one terminal connected to said cathode, a second source of alternating currentpf said low frequency connected between said-cathode and V the other terminal of said phase-shifting netphase-shifting network, and a resistance-capac itance self-biasing means included in said last-;

named connection, said last-named means having a time constant of theorder of the period of said low frequency alternating current, the amplitude of said high frequency signal being small compared to that of either of the low frequency voltages, but sufficient to fire said triode when added to the voltage from said second source.

11. In a control circuit for gas triodes and the like, a gas triode having a grid, a cathode and a plate, means for applying low frequency voltages of like frequency but of unlike phase and'amplitude to the grid-cathode and anode-cathode circuits of said triode, a load device connected to said anode-cathode circuit, means for applying a high frequency signal to said grid-cathodecircuit, and means in said grid-cathode circuitfor developing a self-bias in response to voltages of both said high frequency and said low frequency, the development of said self-bias being modified by the ionization of the gas in said gas triode.

'12. In a control circuit for gastriodes and the like, a gas triode having an input electrode, an output electrode and a third electrode, means connected'to said third electrode for supplying low frequency alternating current voltages of I alternations of said supply voltage, and im pedance means connected in the input circuit of said triode for establishing a unidirectional self bias whose magnitude is substantially proportional to the amplitude of said high frequency signal, said last mentioned means having a time constant so proportioned to the period of said low frequency alternating current that said bias voltage is automatically reduced in response to the ionization of the gas in said triode.

13. In a control circuit for gas triodes and the like, a gas triode having an input electrode, an output electrode and a third electrode, means connected to said third electrode for applying low frequency alternating current voltages of unlike phases and substantially fixed magnitudes to said electrodes, a load device connected to said output electrode, means for applying a high frequency signal to said input electrode, means for automatically biasing said input electrode according to the amplitude of said high frequency signal, and means responsive to the ionization of the gas in said triode for effecting an appreciable reduction in said bias, whereby to effect accurate response of said triode to signals.

ANDREW P. MONTGOMERY. 

